The present invention relates to a logarithmic A/D converter, a logarithmic A/D conversion method, a logarithmic D/A converter, a logarithmic D/A conversion method, and a physical quantity measuring system.
A logarithmic A/D converter has been used to perform A/D conversion on a detection signal that has a wide dynamic range. This is because a logarithmic A/D converter is capable of providing more sufficient resolution for infinitesimal input than a linear A/D converter, and performing A/D conversion on a higher inputted voltage without becoming saturated. Japanese Laid-Open Patent Application H01-158878 discloses an example of such conventional logarithmic A/D converter. FIG. 6 is a circuit diagram showing this conventional logarithmic A/D converter. As shown in the figure, a reference voltage xe2x80x9cVrefxe2x80x9d is applied to a reference voltage terminal 44 of the logarithmic A/D converter, and divided by a plurality of resistors 47 having different resistance so that divided voltages form a progression corresponding to a logarithmic function. Voltage divided by each of the resistors 47 is compared by comparators 42 with an input voltage xe2x80x9cVinxe2x80x9d inputted via an analog input terminal 45. In accordance with a result of this comparison, each of the comparators 42 outputs a logic signal set at either high or low. A decoder 43 converts these logic signals into a digital signal xe2x80x9cDoutxe2x80x9d represented in binary code, and the converted digital signal xe2x80x9cDoutxe2x80x9d is outputted from a digital output terminal 46. In this way, the above conventional A/D converter divides the reference voltage xe2x80x9cVrefxe2x80x9d by using resistors 47 to produce divided voltages that form the logarithmic function progression, and outputs the digital signal xe2x80x9cDoutxe2x80x9d.
A logarithmic A/D converter of the present invention comprises a reference voltage generating unit, a comparison voltage operating unit, and a comparator as described below. The reference voltage generating unit includes at least one first multiplier that raises a predetermine voltage to the nth power to generate a plurality of reference voltages, of which a reference voltage is the nth power of another reference voltage. Based on at least one of the reference voltages, the comparison voltage operating unit generates a comparison voltage. Based on the generated comparison voltage, the comparator generates a digital output value corresponding to a voltage to be converted.
A logarithmic A/D conversion method of the present invention includes the following: generating a plurality of reference voltages, wherein values of the reference voltages have a relation of a progression made by raising the reference voltages to an nth power; generating a plurality of comparison voltages based on at least one of the plurality of reference voltages; and determining an output digital value based on the plurality of comparison voltages. This output digital data corresponds to a voltage to be converted.
A logarithmic D/A converter of the present invention includes a reference voltage generating unit, a selecting unit, and a multiplier. The reference voltage generating unit generates, using a multiplier that raises a predetermined voltage to the nth power, a plurality of reference voltages, of which a reference voltage is the nth power of another reference voltage. Each reference voltage corresponds to a different bit. In accordance with an inputted bit sequence, the selecting unit selects reference voltages. The multiplier performs multiplication using the selected reference voltages to generate an output voltage.
A logarithmic D/A conversion method of the present invention includes the following: raising a predetermined voltage to the nth power to generate reference voltages, of which a reference voltage is the nth power of another reference voltage, and each of which corresponds to a different bit; selecting the reference voltages in accordance with an inputted bit sequence; and performing multiplication using the selected reference voltages to perform D/A conversion.
A physical quantity measuring system according to the present invention includes a logarithmic A/D converter of the present invention.